Configuration of pilot signals by network for enabling comp

ABSTRACT

Example embodiments described herein are directed to systems and methods by which a group of base stations (BS) can configure pilot signals in time and time-frequency, using interference management resources (IMR) and/or channel state information reference signal (CSI-RS) resources, so that the user equipment (UE) such as mobiles and laptops can measure certain possible channel quality indicators (CQI) that correspond to specific channel and interference conditions that can arise during actual data submission. Using these values, example embodiments utilize an interpolation algorithm by which the group of base stations can estimate other possible CQI corresponding to a different set of channel and interference conditions.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. patent application is a continuation-in-part of U.S.application Ser. No. 13/468,316 filed on May 10, 2012, which is fullyincorporated herein by reference in its entirety for all purposes.

BACKGROUND

1. Field

Example embodiments are generally directed to communication networks,and more specifically, wireless communication networks involving servingand collaborating base stations.

2. Related Art

Using coordinated multipoint transmission reception (CoMP) technology, agroup of base stations (BS) can potentially transmit to user equipment(UE). The group of base stations that potentially transmit to a given UEis known as the CoMP cooperating set of the given UE. During actualtransmission, one or more of these BS in the cooperating set cantransmit to a given UE. The other BS in the cooperating set may besilent (e.g., not transmitting) or transmitting to other UEs, which maycause interference to the given UE. The state of each BS (e.g.,transmitting, not transmitting) may change over time. The UE may measurethe channel and interference conditions for a given transmission, sothat the UE can measure the downlink signal to interference plus noiseratio (SINR). The SINR may be used to pick a CQI (channel qualityindicator) value, which is a modulation scheme with a coding rate.

The Long Term Evolution (LTE) transmit signal is two dimensional in timeand frequency, and is composed of multiple time resource elements (RE).Each RE is a two dimensional tile with a duration of roughly 71microseconds in time and a frequency of 15 kilohertz (KHz). For purposesof channel and interference measurement leading to CQI calculation, theBS can configure certain REs with pilot signals. These REs are calledchannel state information reference signal (CSI-RS) resources. Thetransmission can be explained by the following equation which is thereceived signal y in a given CSI-RS resource.y=Hs+I+n  (1)

where H is the channel to be estimated, s is the transmit pilot signalwhich is known at the transmitter and receiver. I+n is the interferenceand noise as measured by the UE, which may include interference fromother BS in the CoMP coordinating set as well as noise and interferencefrom BS outside of the CoMP set. The UE first estimates H from receivedy and from s. Let the estimate be H_(est). The interference I duringchannel estimation is directly proportional to the number of interferingbase stations while the desired base station is transmitting CSI-RS. Forconducting channel estimation, the network may mute the transmissions ofmost of these base stations during CSI-RS transmission. Muting thetransmissions sets I=0, thereby providing an estimate ofinterference-less channel H_(est).

To estimate the interference, related art systems may configure extrapilot symbols in time and frequency called interference managementresources (IMR) to the UE. During IMR transmission, the desired basestation is muted and a subset of the remaining base stations in the CoMPset transmits. The transmission can be explained by the followingequation which is the received signal y in a given IMR.y=I+n

The received signal may assist the UE in estimating the interferenceplus noise power (I+n)est. The estimate for the CQI value is

$\begin{matrix}{{cqi} \approx {\log_{2}\left( {1 + \frac{{{H_{est}*S}}^{2}}{\left( {I + N} \right)_{est}}} \right)}} & (2)\end{matrix}$

The accuracy of the channel estimation tends to increase when theinterference decreases. The theoretical ideal channel estimation occurswhen only the BS whose downlink channel is to be estimated is the onlyBS transmitting, with all of the other BS's in the cooperating set muted(silent, not transmitting). However this channel estimation comes at thecost of inadequate interference measurement. For example, in a casewhere only one BS is transmitting to the UE with the remaining BS's inthe cooperating set being muted, the UE can only measure the backgroundnoise power. The inadequate interference measurement can lead toinaccurate CQI computation for subsequent data transmissions when theother BS in the cooperating set are actually transmitting.

SUMMARY

Aspects of the example embodiments include a base station, whichincludes a central processing unit (CPU) that is configured to determinea plurality of channel quality indicator (CQI) values for a coordinatedmultipoint transmission reception (CoMP) scheme for each user equipment(UE) associated with the base station based on a lower bound CQI valuefor at least one collaborating base station with respect to the each UE,and an upper bound CQI value for the base station with respect to theeach UE, when the base station is serving as a serving base station;and, a front end handling transmissions and receptions between the basestation and the each UE.

The base station may be further configured to transmit firstinstructions for muting ones of the at least one collaborating basestation with a higher signal strength than a first one of the at leastone collaborating base station with respect to the at least one of theUE; transmit second instructions for instructing remaining ones of theat least one collaborating base station to transmit a pilot signal; anddetermine a CQI value of the at least one of the UE as the lower boundCQI value for the first one of the at least one collaborating basestation with respect to the at least one of the UE, when the basestation is serving as the serving base station.

Additional aspects of the example embodiments may further include anon-transitory computer readable medium storing instructions foroperating a base station. The instructions may include determining aplurality of channel quality indicator (CQI) values for a coordinatedmultipoint transmission reception (CoMP) scheme for each user equipment(UE) associated with the base station based on a lower bound CQI valuefor at least one collaborating base station with respect to the each UE,and an upper bound CQI value for the base station with respect to theeach UE, when the base station is serving as a serving base station; andhandling transmissions and receptions between the base station and theeach UE.

The instructions may further involve transmitting first instructions formuting ones of the at least one collaborating base station with a highersignal strength than a first one of the at least one collaborating basestation with respect to the at least one of the UE; transmitting secondinstructions for instructing remaining ones of the at least onecollaborating base station to transmit a pilot signal; and determining aCQI value of the at least one of the UE as the lower bound CQI value forthe first one of the at least one collaborating base station withrespect to the at least one of the UE, when the base station is servingas the serving base station.

Additional aspects of the example embodiments may further include asystem, which involves a serving base station comprising a front endhandling transmissions and receptions between the base station and eachuser equipment (UE) associated with the serving base station, whereinthe serving base station is configured to determine a plurality ofchannel quality indicator (CQI) values for a coordinated multipointtransmission reception (CoMP) scheme for the each UE associated with thebase station based on a lower bound CQI value for at least onecollaborating base station with respect to the each UE, and an upperbound CQI value for the base station with respect to the each UE, whenthe base station is serving as a serving base station; and, the at leastone collaborating base station. The serving base station may be furtherconfigured to transmit first instructions for muting ones of the atleast one collaborating base station with a higher signal strength thana first one of the at least one collaborating base station with respectto the at least one of the UE; transmit second instructions forinstructing remaining ones of the at least one collaborating basestation to transmit a pilot signal; and determine a CQI value of the atleast one of the UE as the lower bound CQI value for the first one ofthe at least one collaborating base station with respect to the at leastone of the UE.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration of a serving base station (BS) inaccordance with an example embodiment.

FIG. 2( a) illustrates a configuration of a collaborating base station,in accordance with an example embodiment.

FIG. 2( b) illustrates a configuration of a collaborating base station,in accordance with an example embodiment.

FIG. 3( a) illustrate a flowchart for the CSI-RS resource configurationmodule, in accordance with an example embodiment.

FIGS. 3( b) to 3(d) illustrate a flowchart for the pilot resourceconfiguration module, in accordance with an example embodiment.

FIG. 4( a) illustrates an example network configuration for illustratingthe flowchart of FIG. 3( a), in accordance with an example embodiment.

FIG. 4( b) illustrates an example network configuration for illustratingthe flowchart of FIGS. 3( b) to 3(d), in accordance with an exampleembodiment.

FIG. 5 illustrates a flowchart for the CQI interpolation module, inaccordance with an example embodiment.

FIG. 6 illustrates a table for CQI values stored in the memory of a BS,in accordance with an example embodiment.

FIG. 7 illustrates a flowchart for a CoMP schedule module in accordancewith an example embodiment.

FIG. 8( a) illustrates a flow diagram of a system in accordance with anexample embodiment.

FIG. 8( b) illustrates a flow diagram of a system in accordance with anexample embodiment.

FIGS. 9( a) and 9(b) illustrate example resource element schedules forbase stations, in accordance with an example embodiment.

FIG. 10 illustrates example resource element schedules for each basestation in a system implementing an example embodiment.

FIG. 11 illustrates a hardware configuration of the base station, inaccordance with an example embodiment.

DETAILED DESCRIPTION

Example embodiments are directed to systems and methods by which a groupof base stations (BS) can configure pilot signals in time andtime-frequency. The pilot signals can include channel state informationreference signal (CSI-RS) resources and/or IMR. The pilot signalsutilized can be CSI-RS resources only, or can be a combination of CSI-RSand IMR. User equipment (UE) such as mobiles and laptops can measurepossible channel quality indicators (CQI) that correspond to specificchannel and interference conditions that can arise during actual datasubmission. Using these values, example embodiments also utilize aninterpolation algorithm by which the group of base stations can estimateother possible CQI corresponding to a different set of channel andinterference conditions. Example embodiments may be implemented inLTE-Advanced cellular networks involving base station cooperationtechnology called coordinated multipoint transmission reception (CoMP).

In an example embodiment where the pilot signals involve only CSI-RS,for each UE, the base station may first determine the order of the basestations per their decreasing downlink signal strength to the UE. Ifthere are N BS for each UE, the base station then configures N+1 CSI-RSresources for each UE wherein each UE measures the channel to each ofthese N BS. In a given resource where a particular downlink channel froma BS is being estimated, a subset of the remaining BS is also configuredto transmit to create interference. This is called partial muting. Thesize of this interfering subset is chosen to be larger for a BS that hasa higher signal strength channel to the UE. This size determination mayallow the UE to measure interferences arising from these BSs and computeCQI of these transmissions.

In an example embodiment where the pilot signals involve both CSI-RS andIMR, for each UE, the base station may first determine the order of thebase stations per their decreasing downlink signal strength to the UE.If there are N BS for each UE, the base station then configures N IMRsand N CSI-RS resources for each UE wherein each UE measures N differentchannel and interference to each of these N BS. For each IMR, a subsetof the remaining BS is also configured to transmit to createinterference. The size of this interfering subset is chosen to be largerfor a BS that has a higher signal strength channel to the UE. This sizedetermination may allow the UE to measure interferences arising fromthese BSs and compute CQI of these transmissions.

By utilizing the ordering of the BS based on downlink signal strength,these signal and interference values may also provide bounds when thesignaling and interfering BS are different, while keeping the number ofsignaling and interfering base stations the same. By using these bounds,example embodiments may utilize a method by which the BS can derive orinterpolate other CQI values.

The example embodiments may be implemented in LTE-Advanced cellularsystems employing CoMP, such as Release 11 (Rel-11) LTE onwards.Implementations of the example embodiments can reduce the feedbackoverhead needed to implement CoMP and can lead to flexibility inimplementing a multitude of CoMP schemes.

Note that if there are N base stations in the cooperating set, any oneor more of these N base stations can transmit to the UE during actualdata transmission. The states of each base station could also changewith time. Thus the UE may need to identify all possible kinds of CQIvalues that correspond to different combinations of signaling andinterfering base stations. However, the total number of such possiblecombinations is large and is exponential with N. The network may not beable to configure so many pilot resources (IMR and CSI-RS resources, orCSI-RS resources only). The example embodiments are thereby directed topermitting the network to configure only N resources (N CSI-RS and Ncorresponding IMR, or only N CSI-RS) from which the UE can measure N+1CQIs and from which other CQIs can also be estimated by the network.

There are two kinds of BSs in the CoMP set. There is the serving BS towhich the UE connects initially, and to which the UE has the highestvalue of downlink received signal strength. There are also the other BSin the CoMP set that collaborate with the serving BS to transmit to theUE. The UE communicates mainly with the serving BS. The serving BS isresponsible for the CoMP functionality (e.g., determining which other BSshould collaborate in CoMP based on UE feedback, how to configure CSI-RSresources for channel estimation) and forwards information to the UE viadownlink control signaling and to the other BS via a backhaul.

FIG. 1( a) illustrates a configuration of a serving base station (BS) inaccordance with an example embodiment. BS within in a system inaccordance with the example embodiments may utilize modules inaccordance with the configuration of FIG. 1( a), when the base stationsare serving as a serving BS. In the example depicted in FIG. 1( a),channel estimation is conducted by sending CSI-RS only.

The serving BS 100 may involve a transceiver (Tx) 101 and a receiver(Rx) 102 module for transmitting to the UE and receiving the signalsfrom the UE and a backhaul module 107 for communicating with other BS.Tx 101 and Rx 102 modules may be implemented in a hardwareconfiguration, such as a radio frequency (R/F) front end as shown inFIG. 11. The serving BS 100 has a radio resource management (RRM) module103 for generating signals utilizing RRM measurement which determinesthe link gain (path loss, shadowing etc.) of each BS to the UE. Theserving BS 100 has a CoMP module 104 for CoMP functionality, a CPU 105for implementing digital signal processing of the LTE signal as well asbeing configured to execute the sub-modules of the CoMP module 104, anda memory 106 that supports the modules of the serving BS 100. Theserving BS 100 may also include a backhaul module 107 for communicatingwith other base stations via a backhaul. The serving BS module 100 mayfurther utilize a CoMP scheduler module 108, for jointly performingscheduling with all BS in the CoMP set. Further details about the CoMPscheduler module 108 are provided in the description for FIG. 7.

The CoMP module 104 of the serving BS 100 may further include thefollowing additional sub-modules:

The CoMP set determination module 104-1 determines whether other BSshould be in the CoMP set of a given UE based on the reported RRMmeasurement values from the UE. The CoMP set determination module 104-1may also rank the serving BS 100 itself as well as the collaborating BSin decreasing order of signal strengths to the UE.

The CSI-RS resource configuration module 104-2 determines, for all BS inthe CoMP set, which REs the BS should transmit pilot signals or mutetheir transmission, and with what corresponding power level. Furtherdetails about the CSI-RS configuration resource configuration module areprovided in the description for FIG. 3.

The CSI-RS resource generation module 104-3 generates the CSI-RS pilotsignals for the serving BS.

The CQI interpolation module 104-4 receives CQI values reported by theUE and interpolates the CQI for other configurations (corresponding todifferent signaling and interfering BS). Further details about the CQIinterpolation module are provided in the description for FIG. 5.

FIG. 1( b) illustrates a configuration of a serving base station (BS) inaccordance with an example embodiment. BS within in a system inaccordance with the example embodiments may utilize modules inaccordance with the configuration of FIG. 1( b), when the base stationsare serving as a serving BS. In the example of FIG. 1( b), channelestimation is done using a combination of CSI-RS and IMR. Thedescription of similar elements in FIG. 1( a) are omitted for clarity.

The pilot resource configuration module 104-2 a determines, for all BSin the CoMP set, which REs the BS should transmit pilot signals or mutetheir transmission, and with what corresponding power level. The pilotsignal refers to IMR for interference measurements and CSI-RS forchannel estimation, or CSI-RS for both interference and channelestimation. Further details about the pilot configuration resourceconfiguration module are provided in the description for FIG. 3(b)-3(d).

The pilot resource generation module 104-3 a generates the CSI-RS andIMR signals (or CSI-RS only) for the serving BS.

FIG. 2( a) illustrates a configuration of a collaborating base station200, in accordance with an example embodiment. BS in a system inaccordance with the example embodiments may utilize modules with theconfiguration of FIG. 2( a), when the BS are serving as a collaboratingBS. In the example depicted in FIG. 2( a), channel estimation isconducted by only using CSI-RS.

Because a BS may serve as either a serving BS 100 or a collaborating BS200 at any given time, redundant elements and descriptions thereof areomitted for clarity. The BS in the CoMP set that are not serving as theserving BS (hence called a collaborating BS) may utilize a configurationas shown in FIG. 2( a). As a collaborating base station 200, modulesspecific to the serving BS 100 such as CoMP set determination 104-1 andCSI-RS configuration modules 104-2 are not utilized, and are omitted forclarity. The CoMP module 204 at the collaborating base station 200 mayutilize a CSI-RS resource configuration initialization module 204-2 forinitializing the CSI-RS resource configuration based on the CSI-RSconfigurations reported by the serving BS.

The UE receives RRM signals from all BS in its CoMP set and performs RRMmeasurements, on which the serving BS ranks all the BS in terms ofdecreasing signal strength. Based on the CSI-RS pilot signals that aretransmitted by all the BS, the UE calculates the signal and interferencevalues, calculates the CQI, and reports the calculated CQI back to theserving BS.

FIG. 2( b) illustrates a configuration of a collaborating base station200, in accordance with an example embodiment. BS in a system inaccordance with the example embodiments may utilize modules with theconfiguration of FIG. 2( b), when the BS are serving as a collaboratingBS. Because a BS may serve as either a serving BS 100 or a collaboratingBS 200 at any given time, redundant elements and descriptions thereofare omitted for clarity.

In the example depicted in FIG. 2( b), channel estimation is conductedby using a combination of CSI-RS and IMR in the pilot signal. Thus, theCSI-RS resource configuration module 204-2 is replaced by a pilot signalconfiguration initialization module 204-2 for initializing the pilotsignal configuration based on the pilot configurations reported by theserving BS.

FIG. 3( a) illustrates a flowchart for the CSI-RS resource configurationmodule 104-2, in accordance with an example embodiment. For eachtransmitting BS, the set of interfering BS may need to be determined. Asmentioned above, a stronger channel quality may tolerate higherinterference and still provide a good estimate for the channel withrespect to interference.

As disclosed above, the serving BS 100 orders the BS by decreasingsignal strength, in a CoMP set of N BSs. Thus, if BS k is thetransmitting BS, then BS 1 to k−1 have stronger signals to the UE andare muted, as otherwise the transmission of such BSs' might causeinterference stronger than the desired signal. This can be assumed fordata transmission and hence also used in the CSI-RS process.

BSs k+1 to N have weaker signal strengths with respect to the BS and maybe included in the interference terms. A subset of these BS willtransmit. At 301, the CSI-RS resource configuration module 104-2determines the subset. The set of transmitting BS where BS k is the BScarrying signal is denoted as Sk. Then the remaining BS i.e. {1, . . .N}-Sk do not transmit (are muted).

The flow at 301 and 302 is iterated for each BS until each of the N BSis configured. After these N CSI-RS resources are configured(corresponding to each of the N BS) the network also configures anotherCSI-RS resource where only BS 1 (the strongest BS and the serving BS)transmits and all others are muted, as shown at 303. The transmission ofBS 1 serves as the upper bound for all achievable throughputs for allother combinations of signaling and interfering BS, wherein CQI valuesfor various subsets are interpolated based on the upper bound.

FIGS. 3( b) to 3(d) illustrate a flowchart for the pilot signal resourceconfiguration module 104-2 a, in accordance with an example embodiment.FIG. 3( b) illustrates that the pilot signal resource configurationmodule 104-2 a may invoke a CSI-RS configuration module 304 and a IMRconfiguration module 305.

FIG. 3( c) illustrates the CSI-RS configuration module 304 that can beinvoked by a pilot signal configuration module 104-2 a. At 304-1, foreach BS k, the CSI-RS configuration module is configured to sendinstructions to transmit a CSI-RS signal. At 304-2, the CSI-RSconfiguration module is configured to send instructions to muteremaining BS in the CoMP set to provide a channel estimation of BS k.

As in the case of FIG. 3( a), for each transmitting BS, the set ofinterfering BS may need to be determined. As mentioned above, a strongerchannel quality may tolerate higher interference and still provide agood estimate for the channel with respect to interference.

As in the case of FIG. 3( a), the serving BS 100 orders the BS bydecreasing signal strength, in a CoMP set of N BSs. Thus, if BS k is thetransmitting BS, then BS 1 to k−1 have stronger signals to the UE andare muted, as otherwise the transmission of such BSs' might causeinterference stronger than the desired signal. This can be assumed fordata transmission and hence also used when using both IMR and CSI-RSresources for channel estimation.

BSs k+1 to N have weaker signal strengths with respect to the BS and maybe included in the interference terms. A subset of these BS willtransmit.

FIG. 3( d) illustrates the IMR configuration module 306 that can beinvoked by a pilot signal configuration module 104-2 a. In an exampleembodiment where the pilot signal can be both CSI-RS and IMR, at 305-1,the IMR configuration module determines the subset. The set oftransmitting BS where BS k is the BS carrying signal is denoted as Sk.Then the remaining BS i.e. {1, . . . N}-Sk do not transmit (are muted)at 305-2. The muted BS also includes the serving BS k so that the UE candirectly measure the interference. Thus, the last IMR is configured sothat all the BS in the CoMP set are muted, which allows the UE tomeasure interference and noise originating from outside the CoMP set.

Thus N CSI-RS resources are configured corresponding to each of the N BSand the UE measures the channel for each of them. N IMRs are alsoconfigured with each IMR associated with a CSI-RS transmission so thatthe UE can measure a corresponding interference. From thesemeasurements, the UE can determine N+1 CQI values which can be reportedback to the serving BS.

FIG. 4( a) illustrates an example network configuration for illustratingthe flowchart of FIG. 3( a), in accordance with an example embodiment.

In an example of the flowchart for FIG. 3( a), assume that there are N=3BS in the CoMP set, with one serving BS 400 (referred herein as BS 1)and two collaborating BSs 401 and 402 (referred herein as BS 2 and BS 3,respectively). The example network configuration is shown in FIG. 4( a).

Thus, the order of the BS in terms of decreasing signal strength to UEis {BS 1, BS 2, BS 3}. When BS 1 transmits CSI-RS 1 403, BS 1 acts asthe signal and BS 2 and BS 3 act as interference. When BS 2 transmits404, only BS 3 acts as interference and BS 1 is muted. When BS 3transmits 405, BS 1 and 2 are muted. Thus set S1={BS 1, BS 2, BS 3}, setS2={BS 2, BS 3} and set S3={BS 3}. In set Sk, BS k is the BS with signaland remaining are interferers. Thus the serving BS 1 configures BS 2 andBS 3 to transmit CSI-RS. The received signal by the UE in the 3 CSI-RSresources arey ₁ =H ₁ s ₁ +I ₂ +I ₃ +zy ₂ =H ₂ s ₂ +I ₃ +Zy ₃ =H ₃ s ₃ +z  (3a)

FIG. 4( b) illustrates an example network configuration for illustratingthe flowchart of FIG. 3( b)-(d), in accordance with an exampleembodiment.

The example is the same as that of FIG. 4( a) with the exception of thetransmission of pilot signals 403-1. 404-1 and 405-1 instead of CSI-RS.

The serving BS 1 configures BS 2 and BS 3 to transmit CSI-RS. When BS 1transmits CSI-RS k, the other BS are muted. The network configures N=3CSI-RS signals as follows:y _(CSI-RS-1) =H ₁ s ₁ +zy _(CSI-RS-2) =H ₂ s ₂ +zy _(CSI-RS-3) =H ₃ s ₃ +z  (3b)

This enables the UE to estimate the channels for BS 1, BS 2 and BS 3.Now the network configures N=3 IMRs. During actual data transmission,when BS 1 transmits 403-1 the data signal, BS 2 and BS 3 can act asinterference. When BS 2 transmits 404-1 only BS 3 acts as interferenceand BS 1 is muted. When BS 3 transmits 405-1, BS 1 and 2 are muted. Thusset S1={BS 2, BS 3}, set S2={BS 3} and set S3={Null}. The receivedsignal by the UE in the 3 IMRs arey _(IMR-1) =I ₂ +I ₃ +zy _(IMR-2) =I ₃ +zy _(IMR-3) =z  (3c)

with N be the measured power of z (e.g. interference and noiseoriginating from outside the CoMP set).

With the help of the above calculations (either from formula 3(a) orfrom formulas 3(b) and 3(c)), the UE can determine the following CQIs

$\begin{matrix}{{{c_{1} \approx {\log_{2}\left( {1 + \frac{{{H_{1}*S_{1}}}^{2}}{I_{2} + I_{3} + N}} \right)}}c_{2} \approx {\log_{2}\left( {1 + \frac{{{H_{2}*S_{2}}}^{2}}{I_{3} + N}} \right)}}c_{3} \approx {\log_{2}\left( {1 + \frac{{{H_{3}*S_{3}}}^{2}}{N}} \right)}} & (4)\end{matrix}$

The UE is configured to report another CQI corresponding to thesituation where the serving BS 1 transmits and all BS within CoMP setare muted. This will give an upper bound to achievable CQI by the UE (asBS 1 has the strongest signal and this CQI computation assumes nointerference from other CoMP set BSs). In the examples of FIGS. 4( a)and 4(b), the serving BS 400, BS 1 also configures another CSI-RSresource where only BS 1 transmits, and the corresponding CQI calculatedby the UE is

$\begin{matrix}{c_{{ma}\; x} \approx {\log_{2}\left( {1 + \frac{{{H_{1}*S_{1}}}^{2}}{N}} \right)}} & (5)\end{matrix}$

From the above formula set (4) and from formula (5), the CQI can beinterpolated for other base station configurations (e.g., BS 2 transmitswith BS 3 muted, etc.), based on a weighting. The weight may beadjusted, or a weighing system may be created by one of ordinary skillin the art to obtain a desired accurate level of estimation for a CQIvalue based on the system configuration.

FIG. 5 illustrates a flowchart for the CQI interpolation module 104-4,in accordance with an example embodiment. The CQI interpolation module104-4 performs the CQI interpolation at the serving base station. WhenBS 1 is transmitting, there are 2 CQIs (c1 and cmax) and for all otherBS k transmitting there is one (ck). The CSI-RS transmission is used forchannel estimation, as noted above. However, several situations canoccur during an actual data transmission, as described below.

When BS k is transmitting, any of the remaining k+1 to N BS may alsotransmit and act as interference. Thus, the CQI value may notnecessarily be based on the set {Sk}-k as had been the case duringCSI-RS or pilot signal transmission. For example, during actualtransmission, BS 1 might be transmitting and BS 2 may be muted, leadingto the following supported rate:

$\begin{matrix}{c_{req} \approx {\log_{2}\left( {1 + \frac{{{H_{1}*S_{1}}}^{2}}{I_{3} + N}} \right)}} & (6)\end{matrix}$

This CQI has to be predicted from c1, c2, c3, and cmax. However, it canbe assumed that BS 1 to k−1 is muted during data transmission of BS k asotherwise strong interference would be created.

As shown by the flowchart of FIG. 5, at 500, the reported CQIs by thefirst N resources are collected. Denote these CQIs as c1, c2, . . . ,cN. The CQI reported by the last resource (where only BS 1, or theserving base station is transmitting), is denoted as cmax.

At 501, the ranges αi are chosen to interpolate CQI values based on thereported CQI values, such that αi=(0, αimax), where αimax=1 for i=1, andα1max>α2max> . . . >αNmax. αi reflects a weight for interpolating CQIvalues of various base station configurations based on received values.Higher potential interference would imply a lower CQI, which wouldresult in selecting a lower weight value. A higher weight value impliesthat less interference is present, thereby resulting in a higher CQI.The weights may be determined by any method of one of ordinary skill inthe art based on the reported CQI values and the system configuration toobtain a good enough estimate. In the example provided, the αimax arederived based on the reported CQI values of c1, c2, c3, . . . cmax, andvarious values of αi are then derived to interpolate the various CQIvalues.

At 502, the transmitting BS is determined and set as BS k. The parameterαkmax for BS k is determined with α1max=1 and α1max>α2max> . . . >αNmax.

At 503, for any BS k, the CQI interpolation module decides the number ofBS to transmit and create interference. Let this number be Nk, and choseαk=(0, αkmax) such that αk is lower for higher Nk. (or higher for higherMk=|Sk|−Nk).

At 504, the CQI interpolation module interpolates various CQI values as(1-αk)ck+αk*cmax, with αk increasing with Mk, based on the derived αivalues as described above.

As an example, suppose k=1 and only BS 3 is transmitting, which rendersNk=1. Thus the CQI is going to be closer to the upper bound (cmax) thanthe case when both BS 2 and BS 3 are transmitting (i.e., c1).

In an additional example, suppose the determination is changed to BS 2and assume BS 3 is not transmitting. The CQI that BS 2 can achieve isstill upper bounded by cmax but may not equal cmax, because H1 hashighest channel power value, which is higher than H2. Hence in theformula for CQI interpolation α2max<1.

FIG. 6 illustrates a table for CQI values stored in the memory of a BS,in accordance with an example embodiment. The BSs maintain tables intheir memory modules as shown in FIG. 6. These tables store differentvalues of CQI. Some of these values may be reported by the UE (e.g.,such as c1, c2, c3, cmax) while others may be interpolated by the CQIinterpolation submodule as explained in FIG. 5. These tables aresubsequently accessed by the CoMP scheduler module.

FIG. 7 illustrates a flowchart for a CoMP schedule module 108 inaccordance with an example embodiment.

In the CoMP scheduler module 108, the different BSs perform joint CoMPscheduling. Thus the CoMP scheduler module 108 is present in allBS—serving and collaborating. At 700 and 701, the scheduler readsdifferent CQI values from the tables mentioned in FIG. 6, along withvalues of average rates of all UEs. The schedule may read these valuesin any order, and is not limited to the example of FIG. 7.

At 702, the scheduler derives new CQI values for other CoMP schemes. Thescheduler may traverse all available CoMP schemes or a subset of them toreduce complexity. At 703, the scheduler calculates the proportionalfair (PF) metric for all UEs that are used for scheduling. For example,if a MU-MIMO or a JT-CoMP scheme is desired, then the scheduler modifiesthe CQI values in the memory table (FIG. 6) to reflect the effects ofthe signal processing. This is jointly done at each BS for all of theUEs. At 704, the schedule selects a subset of UEs for scheduling and aCoMP scheme per a scheduling criterion (e.g., PF or PF plus greedy,etc.)

FIG. 8( a) illustrates a system diagram in accordance with an exampleembodiment. In the example provided in FIG. 8, a serving BS 100interacts with a collaborating BS 200 and a UE 300. The configuration inFIG. 8 is exemplary and the example embodiments are not limited to theconfiguration depicted in FIG. 8. One skilled in the art will recognizethat the serving BS may serve multiple UEs, and there may be multiplecollaborating BS as well as other BS in the system.

The UE 300 may utilize an RRM module 303, a CSI-RS resourceconfiguration initialization module 304-2, a memory 306 and a CQIestimation module 307.

RRM module 303 processes radio resource management reference signals(RRM-RS) from the serving base station 100, the collaborating basestation 200, and possibly other base stations to assist in determiningthe link gain (e.g., path loss, shadowing etc.) of each BS to the UE.RRM module 303 may respond to the serving base station with an RRMreport, which is processed by the CoMP set determination module 104-1 ofthe serving base station 100. As described in FIG. 1, the CoMP setdetermination module 104-1 determines which base station(s) should be inthe CoMP set of a given UE based on the reported RRM measurement valuesreport from the UE. Based on the determined CoMP set, the CSI-RSresource configuration module 104-2 determines, for all BS in the CoMPset, which REs the BS should transmit pilot signals or mute theirtransmission, and with what corresponding power level, as depicted inthe flowchart of FIG. 3( a). Information regarding the configurationdetermined by the CSI-RS resource configuration module is thentransmitted to the UE 300 and the collaborating BS 200, to be processedby CSI-RS resource configuration initialization modules 304-2, 204-2.

The serving BS 100 transmits a CSI-RS from the CSI-RS signal generationmodule 104-3, to UEs associated with the serving BS 100. UE 300processes the received CSI-RS and estimates the CQI to the serving BS100 based on the received CSI-RS by a CQI estimation module 307. The UE300 may also estimate the CQI from received CSI-RS from other basestations, such as the collaborating BS 200. The UE 300 then forwards areport of the estimated CQI values to the serving BS 100, which storesthe values into memory 106. Based on the received values, the serving BS100 utilizes a CQI interpolation module 104-4 to interpolate CQI valuesfor configurations that were not provided by the UE report and storesthem into memory, as depicted in the flowchart of FIG. 5. Based on theinterpolated and stored CQI values, the serving BS determines a CoMPscheme and a schedule with the CoMP scheduler module 108, which it maytransmit to other BS (e.g., collaborating BS 200) by a backhaul 800.

FIG. 8( b) illustrates a system diagram in accordance with an exampleembodiment. The example of FIG. 8( b) is the same as FIG. 8( a) withmodules configured for pilot signal transmission rather than CSI-RS onlytransmission. In the example provided in FIG. 8( b), a serving BS 100interacts with a collaborating BS 200 and a UE 300. The configuration inFIG. 8( b) is exemplary and the example embodiments are not limited tothe configuration depicted in FIG. 8( b). One skilled in the art willrecognize that the serving BS may serve multiple UEs, and there may bemultiple collaborating BS as well as other BS in the system.

The UE 300 may utilize an RRM module 303, a pilot signal configurationinitialization module 304-2 a, a memory 306 and a CQI estimation module307.

RRM module 303 processes radio resource management reference signals(RRM-RS) from the serving base station 100, the collaborating basestation 200, and possibly other base stations to assist in determiningthe link gain (e.g., path loss, shadowing etc.) of each BS to the UE.RRM module 303 may respond to the serving base station with an RRMreport, which is processed by the CoMP set determination module 104-1 ofthe serving base station 100. As described in FIG. 1( b), the CoMP setdetermination module 104-1 determines which base station(s) should be inthe CoMP set of a given UE based on the reported RRM measurement valuesreport from the UE. Based on the determined CoMP set, the pilot signalconfiguration module 104-2 determines, for all BS in the CoMP set, whichREs the BS should transmit pilot signals or mute their transmission, andwith what corresponding power level, as depicted in the flowchart ofFIG. 3( b)-(d). Information regarding the configuration determined bythe pilot signal configuration module is then transmitted to the UE 300and the collaborating BS 200, to be processed by pilot signalconfiguration initialization modules 304-2 a, 204-2 a.

The serving BS 100 transmits a pilot signal from the pilot signalgeneration module 104-3 a, to UEs associated with the serving BS 100. UE300 processes the received pilot signal and estimates the CQI to theserving BS 100 based on the received pilot signal by a CQI estimationmodule 307. The UE 300 may also estimate the CQI from received pilotsignal from other base stations, such as the collaborating BS 200. TheUE 300 then forwards a report of the estimated CQI values to the servingBS 100, which stores the values into memory 106. Based on the receivedvalues, the serving BS 100 utilizes a CQI interpolation module 104-4 tointerpolate CQI values for configurations that were not provided by theUE report and stores them into memory, as depicted in the flowchart ofFIG. 5. Based on the interpolated and stored CQI values, the serving BSdetermines a CoMP scheme and a schedule with the CoMP scheduler module108, which it may transmit to other BS (e.g., collaborating BS 200) by abackhaul 800.

FIG. 9( a) illustrates an example implementation of a resource elementschedule with respect to a transmission of a pilot signal (CSI-RS onlyas noted in FIGS. 1( a), 3(a), and 4(a)), in accordance with an exampleembodiment. Referring to FIG. 4( a), when BS 1 transmits CSI-RS 1, BS 1is treated as the signal and BS 2 and BS 3 act as interference. When BS2 transmits, BS 2 is treated as the signal, BS 3 acts as interferenceand BS 1 is muted. When BS 3 transmits, BS 1 and 2 are muted. From thisexample, set S1={BS 1, BS 2, BS 3}, set S2={BS 2, BS 3} and set S3={BS3}. In set Sk, BS k is the BS with signal and the remaining BS areinterferers. The serving BS 1 configures BS 2 and BS 3 to transmitCSI-RS according to a resource element schedule with respect tofrequency and time, an example of which is shown in FIG. 9( a). Theschedule may instruct the BS to transmit data at certain resourceelements and CSI-RS at other resource elements. The received signal bythe UE in the 3 CSI-RS resources arey ₁ ^(a) =H ₁ s _(CSI-RS-1) +H ₂ s _(CSI-RS-2) +H ₃ s _(CSI-RS-3) +zy ₂ ^(a) =H ₂ s _(CSI-RS-2) +H ₃ s _(CSI-RS-3) +zy ₃ ^(a) =H ₃ s _(CSI-RS-3) +z

With the help of the received signals, the UE may then estimate thechannelsĤ ₁ ^(a) =f(y ₁ ^(a))Ĥ ₂ ^(a) =f(y ₂ ^(a))Ĥ ₃ ^(a) =f(y ₃ ^(a))

Errors in channel estimation can arise due to the interfering CSI-RSsignals from other base stations. From these values the UE estimates thefollowing interference measurementsÎ ₁ ^(a) =y ₁ −Ĥ ₁ ^(a) s _(CSI-RS-1)Î ₂ ^(a) =y ₂ −Ĥ ₂ ^(a) s _(CSI-RS-2)Î ₃ ^(a) =y ₃ −Ĥ ₃ ^(a) s _(CSI-RS-3)

The interference estimated may be due to the other BS transmittingCSI-RS signals, which may be different from interference caused due todata transmission. Hence there may be inaccuracies in estimatinginterference from using CSI-RS, although the signaling overhead ofutilizing CSI-RS alone may be lower than the signaling overhead of acombination of CSI-RS and IMR. From these values the UE estimates thefollowing CQIs,

$c_{1}^{a} \approx {\log_{2}\left( {1 + \frac{{{{\hat{H}}_{1}^{a}s_{1}}}^{2}}{{\hat{I}}_{1}^{a}}} \right)}$$c_{2}^{a} \approx {\log_{2}\left( {1 + \frac{{{{\hat{H}}_{2}^{a}s_{2}}}^{2}}{{\hat{I}}_{2}^{a}}} \right)}$$c_{3}^{a} \approx {\log_{2}\left( {1 + \frac{{{{\hat{H}}_{3}^{a}s_{3}}}^{2}}{{\hat{I}}_{3}^{a}}} \right)}$FIG. 9( b) illustrates an example implementation of a resource elementschedule with respect to a transmission of a pilot signal (CSI-RS or IMRas noted in FIGS. 1( b), 3(b)-(d) and 4(b)), in accordance with anexample embodiment. Referring to the example of FIG. 4( b), when BS ktransmits CSI-RS k, the others are muted. From the example of FIG. 4(b), the network configures N=3 CSI-RS signals as followsy ₁ ^(b) =H ₁ s _(CSI-RS-1) +zy ₂ ^(b) =H ₂ s _(CSI-RS-2) +zy ₃ ^(b) =H ₃ s _(CSI-RS-3) +z

From the received signals, the UE to estimate the channels H₁, H₂ andH₃.Ĥ ₁ ^(b) =f(y ₁ ^(b))Ĥ ₂ ^(b) =f(y ₂ ^(b))Ĥ ₃ ^(b) =f(y ₃ ^(b))

The estimation of the channels may be better than utilizing only CSI-RSas shown in the example of FIG. 9( a), however, the signaling overheadmay be greater. In this example Ĥ₁ ^(b) may be a better estimate of H₁than Ĥ₁ ^(a) and similarly for the other channels.

Now the network configures N=3 IMRs. During actual data transmission,when BS 1 is signal and BS 2 and BS 3 can act as interference. Duringactual data transmission, when BS 2 transmits only BS 3 can act asinterference and BS 1 will be muted. When BS 3 transmits, BS 1 and 2 aremuted. Thus set S1={BS 2, BS 3}, set S2={BS 3} and set S3={Null}. Thereceived signal by the UE in the 3 IMRs arey _(IMR-1) =I ₂ +I ₃ +zy _(IMR-2) =I ₃ +zy _(IMR-3) =z

The estimation of interference from using a pilot signal implementationmay be improved over using CSI-RS alone, as the actual data interferenceis measured directly. Let N be the measured power of z, the out of CoMPset interference plus noise. With the help of these the UE can determinethe following CQIs

$c_{1}^{b} \approx {\log_{2}\left( {1 + \frac{{{{\hat{H}}_{1}^{b}s_{1}}}^{2}}{I_{2} + I_{3} + N}} \right)}$$c_{2}^{b} \approx {\log_{2}\left( {1 + \frac{{{{\hat{H}}_{2}^{b}s_{2}}}^{2}}{I_{3} + N}} \right)}$$c_{3}^{b} \approx {\log_{2}\left( {1 + \frac{{{{\hat{H}}_{3}^{b}s_{3}}}^{2}}{N}} \right)}$

Thus the estimates of the CQIs may be improved.

FIG. 10 illustrates example resource element schedules for each basestation in a system implementing an example embodiment.

With reference to FIGS. 4( a) and 4(b), a resource element schedule canbe provided for a serving base station and a collaborating base stationin accordance with an example embodiment. Referring to FIGS. 9( a) and9(b), the base stations can transmit data signals for resource elementsthat do not involve IMR or CSI-RS. When a base station is configured totransmit a pilot signal, example systems can determine if the pilotsignal for a given resource element is to be CSI-RS or IMR. If theresource element is indicated as CSI-RS, the other base stations in theCoMP set may thereby be muted to allow for channel estimation. If theresource element is IMR, base stations with a stronger signal strengthare muted, and base stations with a weaker signal strength continue totransmit data signals.

FIG. 11 illustrates an exemplary hardware configuration for a basestation, in accordance with an example embodiment.

A base station 900 may utilize a transceiver module 901, a basebandsignal processing module 902, and one or moreAnalog-Digital/Digital-Analog converters 904 for performing the modulesdescribed in FIG. 1 and FIG. 2. The transceiver module 901 may include atransmitter 901-1 and a receiver 901-2 for handling transmissions andreceptions to the base station 900. The transceiver module 901 may be inthe form of a radio frequency (R/F) front end as a hardwareconfiguration.

The baseband signal processing module 902 may include a centralprocessing unit (CPU) 902-1 and a memory 902-2.

Signals between the transceiver module 901 and the baseband signalprocessing module 902 may be processed by one or moreAnalog-Digital/Digital-Analog converters 904 through one or moreinterfaces 903.

The exemplary hardware configuration may be utilized for any of theserving base station 100 as depicted in FIG. 1 and the collaboratingbase station 200 as depicted in FIG. 2. For example, the baseband signalprocessing module 902 including the CPU 902-1 and memory 902-2 may beused to process the various modules such as CoMP modules 104, 204, aswell as the CoMP scheduler modules 108, 208 and the RRM modules 103, 203as depicted in FIG. 1 and FIG. 2. Communication via the backhaul modules107, 207 may also be conducted through the baseband signal processingmodule 902 to facilitate communications through the backhaul.

Similar Tx modules 101, 201, and Rx modules 102, 202 may be implementedas a transceiver module 901 in the form of a radio frequency (R/F) frontend. Various hardware configurations of transmitter 901-1 and receiver902-2 may be utilized for facilitating communication with UEs. Further,the configuration of base station 900 is not limited to a radiofrequency front end. One of ordinary skill in the art would be able toimplement any type of physical front end as needed to facilitatecommunication between the base station and the UEs.

Finally, some portions of the detailed description are presented interms of algorithms and symbolic representations of operations within acomputer. These algorithmic descriptions and symbolic representationsare the means used by those skilled in the data processing arts to mosteffectively convey the essence of their innovations to others skilled inthe art. An algorithm is a series of defined steps leading to a desiredend state or result. In the example embodiments, the steps carried outrequire physical manipulations of tangible quantities for achieving atangible result.

Unless specifically stated otherwise, as apparent from the discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing,” “computing,” “calculating,” “determining,”“displaying,” or the like, can include the actions and processes of acomputer system or other information processing device that manipulatesand transforms data represented as physical (electronic) quantitieswithin the computer system's registers and memories into other datasimilarly represented as physical quantities within the computersystem's memories or registers or other information storage,transmission or display devices.

The example embodiments may also relate to an apparatus for performingthe operations herein. This apparatus may be specially constructed forthe required purposes, or it may include one or more general-purposecomputers selectively activated or reconfigured by one or more computerprograms. Such computer programs may be stored in a computer-readablestorage medium, such as, but not limited to optical disks, magneticdisks, read-only memories, random access memories, solid state devicesand drives, or any other types of media suitable for storing electronicinformation. The algorithms and displays presented herein are notinherently related to any particular computer or other apparatus.

Various general-purpose systems may be used with programs and modules inaccordance with the teachings herein, or it may prove convenient toconstruct a more specialized apparatus to perform desired method steps.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein. The instructions of theprogramming language(s) may be executed by one or more processingdevices, e.g., central processing units (CPUs), processors, orcontrollers.

As is known in the art, the operations described above can be performedby hardware, software, or some combination of software and hardware.Various aspects of example embodiments of the invention may beimplemented using circuits and logic devices (hardware), while otheraspects may be implemented using instructions stored on a non-transitorycomputer readable medium, which if executed by a processor, would causethe processor to perform a method to carry out various exampleembodiments. Furthermore, some example embodiments may be performedsolely in hardware, whereas other example embodiments may be performedsolely in software. Moreover, the various functions described can beperformed in a single unit, or can be spread across a number ofcomponents in any number of ways. When performed by software, themethods may be executed by a processor, such as a general purposecomputer, based on instructions stored on a computer-readable medium. Ifdesired, the instructions can be stored on the medium in a compressedand/or encrypted format.

Moreover, other implementations of the example embodiments will beapparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. Variousaspects and/or components of the described example embodiments may beused singly or in any combination. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the example embodiments being indicated by the followingclaims.

What is claimed is:
 1. A base station, comprising: a central processingunit (CPU) that is configured to: when the base station is serving as aserving base station, determine a plurality of channel quality indicator(CQI) values for a coordinated multipoint transmission reception (CoMP)scheme for each user equipment (UE) associated with the base stationbased on a lower bound CQI value for at least one collaborating basestation within a CoMP set of the base station with respect to at leastone of the UE, the at least one collaborating base station configured totransition from a collaborating base station to the serving base stationaccording to the CoMP scheme, and an upper bound CQI value for the basestation with respect to the each UE for the base station serving as theserving base station; transmit first instructions for muting ones of theat least one collaborating base station with a higher signal strengththan a first one of the at least one collaborating base station withrespect to the at least one of the UE; transmit second instructions forinstructing remaining ones of the at least one collaborating basestation to transmit a pilot signal; and receive a lower bound CQI valuefor the first one of the at least one collaborating base station withrespect to the at least one of the UE based on the pilot signal; and afront end handling transmissions and receptions between the base stationand the each UE.
 2. The base station of claim 1, wherein when the basestation is serving as the serving base station and when a resourceelement of the pilot signal is IMR, the CPU is further configured to:mute transmission of the serving base station for the resource element;and transmit third instructions for the remaining ones of the at leastone collaborating base station to transmit a data signal for theresource element.
 3. The base station of claim 1, wherein the CPU isconfigured to determine, with respect to all of the at least onecollaborating base station, one lower bound CQI value for the each UE,and wherein the CPU is further configured to determine one upper boundCQI value for the each UE.
 4. The base station of claim 1, wherein whenthe base station is serving as the serving base station and when aresource element of the pilot signal is a channel state informationreference signal (CSI-RS), the CPU is further configured to: transmitfourth instructions for muting all of the at least one collaboratingbase station; transmit the channel state information reference signal(CSI-RS); and determine a CQI value of the each UE as the upper boundCQI value for the base station with respect to the each UE.
 5. The basestation of claim 4, wherein when the base station is serving as theserving base station, the CPU is further configured to set an upperbound with respect to the each of the at least one collaborating basestation by utilizing the upper bound of the base station with respect tothe each UE adjusted by a weight, the weight being based on a radioresource management (RRM) measurement for the each of the at least onecollaborating base station, and wherein the CPU is further configured toselect a CoMP scheme based on the determined upper bound for each of theat least collaborating base station with respect to the each UE.
 6. Thebase station of claim 1, wherein the CPU is further configured todetermine if the base station is to serve as the serving base station oras a collaborating base station for the each UE based on a radioresource management (RRM) measurement.
 7. The base station of claim 1,wherein when the base station is serving as a collaborating basestation, the CPU is further configured to process a schedule fortransmitting one of a channel state information reference signal(CSI-RS) and a data signal, or for muting when the at least onecollaborating base station transmits one of the CSI-RS and the datasignal.
 8. A non-transitory computer readable medium storinginstructions for operating a base station, the instructions comprising:when the base station is serving as a serving base station: determininga plurality of channel quality indicator (CQI) values for a coordinatedmultipoint transmission reception (CoMP) scheme for each user equipment(UE) associated with the base station based on a lower bound CQI valuefor at least one collaborating base station within a CoMP set of thebase station with respect to at least one of the UE, the at least onecollaborating base station configured to transition from a collaboratingbase station to the serving base station according to the CoMP scheme,and an upper bound CQI value for the base station with respect to theeach UE for the base station serving as the serving base station;transmitting first instructions for muting ones of the at least onecollaborating base station with a higher signal strength than the firstone of the at least one collaborating base station with respect to theat least one of the UE; transmitting second instructions for instructingremaining ones of the at least one collaborating base station totransmit a pilot signal; and receiving a lower bound CQI value for thefirst one of the at least one collaborating base station with respect tothe at least one of the UE based on the pilot signal and, handlingtransmissions and receptions between the base station and the each UE.9. The non-transitory computer readable medium of claim 8, furthercomprising instructions for determining the lower bound for a first oneof the at least one collaborating base station with respect to the atleast one of the UE, when the base station is serving as the servingbase station and when a resource element of the pilot signal is IMR, theinstructions comprising: muting transmission of the serving base stationfor the resource element; and transmitting third instructions for theremaining ones of the at least one collaborating base station totransmit a data signal for the resource element.
 10. The non-transitorycomputer readable medium of claim 8, further comprising instructions fordetermining the upper bound CQI value for the base station with respectto the each UE, when the base station is serving as the serving basestation and when a resource element of the pilot signal is a channelstate information reference signal (CSI-RS), the instructionscomprising: transmitting fourth instructions for muting all of the atleast one collaborating base station; transmitting the channel stateinformation reference signal (CSI-RS); and determining a CQI value ofthe each UE as the upper bound CQI value for the base station withrespect to the each UE associated with the base station.
 11. Thenon-transitory computer readable medium of claim 8, further comprisinginstructions to determine the upper bound for each of the at least onecollaborating base station with respect to the each UE, when the basestation is serving as the serving base station, the instructionscomprising: setting the upper bound with respect to the each of the atleast one collaborating base station by utilizing the upper bound of thebase station with respect to the each UE adjusted by a weight, theweight being based on a radio resource management (RRM) measurement forthe each of the at least one collaborating base station; wherein thenon-transitory computer readable medium further comprises instructionsto select a CoMP scheme based on the determined upper bound for each ofthe at least collaborating base station with respect to the each UE. 12.The non-transitory computer readable medium of claim 8, furthercomprising instructions for determining if the base station is to serveas the serving base station or as a collaborating base station for theeach UE based on a radio resource management (RRM) measurement.
 13. Thenon-transitory computer readable medium of claim 8, further comprisinginstructions for processing a schedule for transmitting one of a channelstate information reference signal (CSI-RS) and a data signal, or formuting when the at least one collaborating base station transmits one ofthe CSI-RS and the data signal, when the base station is serving as acollaborating base station.
 14. A system, comprising: a serving basestation comprising a front end handling transmissions and receptionsbetween the base station and each user equipment (UE) associated withthe serving base station, wherein the serving base station is configuredto: determine a plurality of channel quality indicator (CQI) values fora coordinated multipoint transmission reception (CoMP) scheme for theeach UE associated with the serving base station based on a lower boundCQI value for at least one collaborating base station within a CoMP setof the base station with respect to at least one of the UE, the at lastone collaborating base station configured to transition from acollaborating base station to the serving base station according to theCoMP scheme, and an upper bound CQI value for the serving base stationwith respect to the each UE; transmit first instructions for muting onesof the at least one collaborating base station with a higher signalstrength than a first one of the at least one collaborating base stationwith respect to the at least one of the UE; transmit second instructionsfor instructing remaining ones of the at least one collaborating basestation to transmit a pilot signal; and receive a lower bound CQI valuefor the first one of the at least one collaborating base station withrespect to the at least one of the UE based on the pilot signal; and,the at least one collaborating base station.
 15. The system of claim 14,wherein when a resource element of the pilot signal is IMR, the servingbase station is further configured to: mute transmission of the servingbase station for the resource element; and transmit third instructionsfor the remaining ones of the at least one collaborating base station totransmit a data signal for the resource element.
 16. The system of claim15, wherein the determining the lower bound CQI value for the first oneof the at least one collaborating base station with respect to the atleast one of the UE is based on a formula of:$\log_{2}\left( {1 + \frac{{{H*S}}^{2}}{I + N}} \right)$ wherein H isa channel matrix of the first one of the at least one collaborating basestation, S is the pilot signal transmitted, I is interference caused bythe remaining ones of the at least one collaborating base station, and Nis noise.
 17. The system of claim 14, wherein when a resource element ofthe pilot signal is a channel state information reference signal(CSI-RS), the serving base station is further configured to: transmitfourth instructions for muting all of the at least one collaboratingbase station; transmit the channel state information reference signal(CSI-RS); and determine a CQI value of the each UE as the upper boundCQI value for the serving base station with respect to the each UE. 18.The system of claim 14, wherein the serving base station is furtherconfigured to set an upper bound with respect to the each of the atleast one collaborating base station by utilizing the upper bound of theserving base station with respect to the each UE adjusted by a weight,the weight being based on a radio resource management (RRM) measurementfor the each of the at least one collaborating base station, and whereinthe serving base station is further configured to select a CoMP schemebased on the determined upper bound for each of the at least onecollaborating base station with respect to the each UE.
 19. The systemof claim 14, wherein the serving base station is further configured todetermine if the serving base station is to serve as the serving basestation or as a collaborating base station for each UE based on a radioresource management (RRM) measurement.
 20. The system of claim 14,wherein the at least one collaborating base station is furtherconfigured to process a schedule for transmitting one of a data signaland a channel state information reference signal (CSI-RS) or for mutingwhen the at least one collaborating base station transmits one of thedata signal and the CSI-RS.